<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var arr =[1,2,3,4,5,6,7];
    var arr2 = arr.fill(8,1,4);
    console.log(arr,arr2);
</script>
</html>